Piston connection for free-piston engine



Nov. 18, 1969 s. E. SORENSEN ET AL PISTON CONNECTION FOR FREE -PISTON ENGINE Original Filed Oct. 22, 1965 SVEND E. SORENSEN WILLIAM L. McHALE INVENTORS BY); 7 mad, 0Z0

United States Patent 3,478,651 PISTON CONNECTION FOR FREE-PISTON ENGINE Svend E. Sorensen, King of Prussia, and William L.

McHale, Broomall, Pa., assignors, by mesne assignments, to The Battelle Development Corporation, Columbus, Ohio, a corporation of Delaware Original application Oct. 22, 1965, Ser. No. 501,719, now Patent No. 3,386,647, dated June 4, 1968. Divided and this application July 12, 1967, Ser. No. 688,281 Int. Cl. F01b 11/02; F021. 3/00 US. Cl. 92-152 1 Claim ABSTRACT OF THE DISCLOSURE The working and power pistons, operating in separate cylinders, of a free piston engine are provided with a universal joint type of construction where the piston rod connects to one of the pistons. The piston that is solidly connected to the piston rod is provided with a soft metal section allowing it to wear in as it reciprocates in its cylinder. This construction allows larger misalignment tolerances between the two cylinders.

Cross-references to related applications This application is a divisional application of our copending application Ser. No. 501,719, entitled Free-Piston Engine Diaphragm Compressor, filed Oct. 22, 1965, now Patent No. 3,3 86,647.

Background of the invention 'This invention relates to a connection for a power and working piston for a free-piston engine. Frequently it is not feasible to use one end of the free-piston as the combustion side and the other end as the total working side. If direct reciprocating motion is to be used at the output, a second piston or working piston is often the workpiece. The guide for the working piston is a second cylinder separate from the combustioncylinder.

In a free-piston engine having a connected working piston, the problem arises in the connection between'the power piston and the working piston. If the connection is solid, then the power cylinder and working cylinder must have very good alignment. and also the power piston and working piston must have equally good alignment. This invention solves the alignment problems by providing a flexible connectionbetween the power piston and the piston rod, allows the working piston to be slightly misaligned (as'suming there is some misalignment in thecylinders), and provides a wear in section on the working piston so that it essentially re-aligns itself inside the working cylinder as the free-piston engine is operated.

Summary of the invention Briefly described, this invention includes a pivotal attachment between the power piston and working piston of a free-piston engine wherein each piston reciprocates in separate cylinders'having their axes substantially aligned thereby allowing minor misalignment of the two'cylinders.

Preferably the constructionfor the pivotal attachment includesa central threaded bore in the power piston; a rod attached to the working piston having an enlarged end that issmaller than the central threaded bore; and a ring slidably positioned around the rod between the enlarged end and the working piston, the ring having a central opening larger than the rod and smaller than the enlarged end, and the ring having peripheral threads engaged with the central threaded bore retaining the enlarged end of the rod in the central bore.

'Another preferred feature of the invention includes a soft metallic surface on the working piston contiguous to,

3,478,651 Patented Nov. 18 1969 "ice the wall of the working cylinder allowing the working piston to wear into proper alignment with the working cylinder.

One object of this invention is to provide a construction wherein the alignment problem for the reciprocating parts of the free-piston engine are largely eliminated.

Another object of this invention is to provide a freepiston engine having a power cylinder and working cylinder that may be slightly misaligned thereby eliminating close tolerances of these parts and reducing manufacturing costs.

, Still another object of this invention is to provide for automatic re-alignment of the working piston and working cylinder when they are slightly misaligned.

Still other objects and advantages of the invention will be apparent from the detailed description of the apparatus, the drawings and the claim that follows.

Brief description of the drawing FIG. 1 is a sectional elevational view of the free-pistonengine diaphragm compressor.

Description of the preferred embodiment Referring to FIG. 1, the free-piston-engine diaphragm compressor 11, includes an engine section 13, and a compressor section 15 that are closely connected. The free piston includes a power piston 17 connected to a compressor piston 19 by means of a piston rod 21. The power piston 17 reciprocates in an engine cylinder 23 having an inner liner 25. The power piston 17, provided with piston rings 27, divides the cylinder 23 into a combustion chamber 29 and a bounce and pumping chamber 31. The engine cylinder 23 is provided with a plurality of fins 3333 for dissipating the heat of the combustion process. Oil, for lubrication of the power piston 17, is provided to a fitting 35 through a passage 37 connected to an oil ring 39 that surrounds the liner 25. The liner 25 is provided with a plurality of ports 41-41 for introducing the oil into the combustion chamber 29.

The cylinder head 43, which is preferably integrally cast with the engine cylinder 23, is provided with a spark plug 45 and a tap-off valve 47. The tap-off valve 47 directs high pressure combustion products from the combustion chamber 29 to a storage tank (not shown) which is a part of the starting system for the free-piston engine 13.

The air and fuel are mixed together and enter, the com-.

take ports 5151 have a slanted entrance passage 55 that directs theair toward the wall of the combustion chamber 29 near the cylinderhead 43 after which the air turns to-' E (The port arrangement shown in FIG. 1 is for convenience only and is not the, actual preferred arrangement.) The exhaust ports, 5353 communicate withanvexhaust passage57 which preferably is connected to a tun'ed'ex-- pansion' chamber (not shown) and a standard two-cycle automotive" enginemufller- (not shown). x

The free-piston-engine diaphragm,compressor 11 is capable of operating with a variety of fuels. The embodiment shown in FIG. 1 is adapted for burning naturalg'as. A carburetor 59 is provided having an air intake opening 61. An annular fuel-air space 63 surrounds the bounce and pumping chamber 31 and communicates with bounce and pumping chamber 31 by means of ports 65 65 that are opened and closed by the trailing edge 67 ofthe piston 17. A passage 69 leads from the carburetor 59 to a reed valve plate 71 that has a plurality of reeds 73-73 that are activated by pressure differences to open and close a plurality of fuel-air ports 75-75.

When the power piston 17 is in the position shown in FIG. 1, the fuel-air space 63 communicates with the combustion chamber 29 through the intake ports 51-51, the intake ports 51-51 being opened when they are uncovered by the leading edge 77 of the power piston 17. As the piston 17 moves toward the cylinder head 43 on the compression stroke, the bounce and pumping chamber 31 becomes larger. (The bounce and pumping chamber 31 is defined by the end of the piston 17 at the trailing edge 67, the cylinder liner 25 and the seal section 79.)

When the trailing edge 67 of piston 17 moves to uncover ports 65-65, the chamber 31, which up to this point was acting as a more or less blind rebound chamber becomes a pumping chamber. At about the same time as ports 65-65 are opened, the leading edge 77 of piston 17 closes the intake ports 5151. The continued enlargement of chamber 31 causes a reduction of pressure in chamber 31 causing the reed valves 73-73 to open and a stoichiometric mixture enters fuel-air space 63 and chamber 31. The mixture continues to enter until the piston 17 reaches top dead point position.

On the return or power stroke, the chamber 31 decreases in size, the valves 73-73 close, and the fuel-air mixture in the fuel-air space 63 is pressurized until the trailing edge 67 of piston 17 recloses port 65. At about the same time, the leading edge 77 opens ports 51-51 allowing the pressurized fuel-air mixture to flow into combustion chamber 29 scavenging the chamber 29 and supplying the fuel-air mixture for the next power stroke. After port 65 is closed, chamber 31 again becomes substantially a blind chamber and the gas compressed therein by the movement of piston 17 cushions the power stroke (along with the action of compressor and supplies rebound energy to drive piston 17 back on the compression stroke.

A compressor cylinder section 81 is attached to the end of the engine cylinder 23 and is provided with a central bore 83 that flares into a bell-shaped section 85. The compressor piston 19 reciprocates in the central bore 83 and acts on a column of fluid 87 (preferably oil) that forms a coupling to transfer the motion of the piston 19 to the diaphragm 89. The central bore 83 is separated from the bounce and pumping chamber 31 by the seal section 79. The seal section 79 includes two interference shaft seals 91-91 that contact the piston rod 21 and substantially prevent leakage between chamber 31 and central bore 83. An annular space 93 is positioned between the seals 91-91 and is vented to the atmosphere through a passage 95 allowing any gases or oil that might leak by the seals 91-91 to escape. The seal section 79 fits against the end 97 of the cylinder lining and against a shoulder 98 formed at the end of the cylinder section 81. Appropriate seals, such as O-ring seals 99-99, are positioned between the various surfaces of the cylinder liner 25, seal section 79, and cylinder section 81. A seal 101 is also provided between the engine cylinder 23 and the compressor cylinder section 81.

Reciprocation of the compressor piston 19 exerts a force on the fluid column 87. On the power stroke of the engine piston 17, the compressor piston 19 forces the fluid through a back-up plate 103 and against the diaphragm 89. The back-up plate 103 is provided with an O-ring type seal 107 and a plurality of substantially radial slots 109-109. The surface 111 mounted toward the diaphragm 89 is concave to provide for the flexations of the diaphragm 89'. The diaphragm 89 ordinarily will not contact the back-up plate 103 at maximum compressor suction stroke (when the compressor piston 19 is at top dead center), but during engine shut-off, the compressor gas pressure forces the diaphragm 89 against the concave surface 111 of back-up plate 103.

During the power stroke of the engine 13, when the piston 19 forces fluid through the back-up plate slots 4 109-109, the diaphragm 89 is moved to force compressor gas through a plurality of discharge valves 113-113 mounted in a valve plate 115. The valve plate 115 is provided with a concave surface that is mounted toward the diaphragm 89. An O-ring type seal 131 is positioned on the valve plate 115. The seal 121 is positioned to be opposite seal 107 on the back-up plate 103 so that the seals 107 and 121 cooperate to hold and seal around the periphery of the diaphragm 89. Adjacent to the seal 107, a groove 123 is provided on the back-up plate 103 and a groove 125 is provided adjacent seal 121 on the valve plate 115, which, together, form an annular space that permits the edge 127 of the diaphragm 89 to flip up and down as the diaphragm 89 flexes to pump the refrigerant gas.

The compressor intake valve 129 is centrally positioned in the valve plate 115. Slightly more area is provided for compressor discharge (six discharge valves 113- 113 are included in the embodiment of valve plate) than for intake since the power stroke of the engine 13 is somewhat faster than the rebound stroke. Two O-ring type seals 131 and 133 are positioned between the valve plate 115 and the compressor manifold 135. The seals 131 and 133 prevent leakage of the discharge gas to the intake gas-side and also leakage of the discharge gas from between the valve plate 115 and compressor manifold 135 to atmosphere.

The compressor manifold 135 is provided with a central inlet manifold 137 surrounded by an annular discharge manifold 139. An inlet line 141 connects the inlet manifold 137 to the evaporator (not shown) and a discharge line 143 connects the discharge manifold to the condenser (not shown).

Much of the expense in engines of this type is due to the alignment, tolerance and wear problems that are usually all closely related. The apparatus of this invention is constructed to avoid and eliminate some of these problems. Since the engine cylinder 23 and compressor cylinder section -81 are made separately and assembled, it follows that if these parts were perfectly aligned, the pistons 17 and 19 must be perfectly aligned. Although care is taken to establish and maintain good alignment, much of the problem is eliminated by a universal joint arrangement between the piston 17 and piston rod 21. The rod 21 fits into a space 145 in the piston 17. A washer 147 fits around the piston rod 21 and a nut 149 is threaded into the piston 17 holding the washer 147 in place. The piston 17 and rod 21 are always in compression (by the combustion gases pushing the piston 17 toward the compressor 15 or the compressor gases pushing the piston 19, via the diaphragm 89 and fluid column 87, toward the cylinder head 43) and the washer 147 is only under very light loads if it is ever loaded at all. However, the important feature of the connection shown is that the piston rod 21 is not firmly attached to the piston 17 so that alignment and tolerance discrepancies are allowable. Further, tolerance of misalignment conditions is allowed by the construction of the compressor piston 19. Since the fluid column 87 is used as a force transfer medium, sealing requirements are not as strict as they would be in other types of refrigerant compressors. When oil is used in the column 87, a leakage rate of about one gallon per hour can be tolerated. The oil merely passes by the piston 19 and out the passage 151 to an oil sump (not shown). A seal 153 is provided around the piston 19 to prevent excessive leakage. The piston 19 is also provided with a sleeve 155 selected from a material that is softer than the material of the piston 19. This feature centers the piston 19 in the bore 83. The addition, the soft material will catch any small foreign particles.

Since oil leakage around the piston 19 is permissible, the fluid lost from the fluid column 87 must be replaced on a regular basis. It was previously stated that the rebound for the engine piston 17 is provided in part by the chamber 31 and in part by the compressor gas exerting pressure on the diaphragm 89 and applying a force on the compressor piston 19 through the fluid column 87. The pressure in the bounce chamber 31 increases as the power stroke lengthens slightly due to a decrease of fluid in the column 87 or greater displacement of the diaphragm 89 due to a decrease in compressor load. The increased pressure in the bounce chamber 31 is used to activate the oil pump 157 which is insensitive to normallength strokes but is activated when the pressure in the bounce chamber 31 increases due to less fluid in the column 87 and the resulting longer piston strokes. A port 159 is provided in the seal section 79 that communicates with the pump 157 through a passage 161.

The pump 157 engages a threaded socket 167 in the cylinder section 81. At the inlet of pump 157 a threaded fitting 171 communicates with the oil sump (not shown). The outlet of pump 157 is connected through a check valve 174 to a tube 175 and supplies make-up oil to the oil column 87.

The oil pump 157 operates when the oil column 87 needs oil. The reduction of oil in the oil column 87 decreases the resistance to the power stroke of piston 17, the power stroke lengthens slightly and the gas compressed in bounce chamber 31 takes on the increased rebound requirements by an increase in pressure. The pump 157 is activated in response to the increased pressure in bounce chamber 31 acting through passage 161, thereby adding oil to oil column 87.

The timing for the ignition system is provided by positioning a pick-up device 223 to be triggered by the edge 225 of piston 19. The pick-up 223 which includes a permanent magnet (not shown), surrounded by a coil (not shown). When the piston edge 225 passes the end of the permanent magnet it breaks magnetic flux lines to produce a small electric current in coil that triggers a high tension circuit (not shown) that fires the spark plug 45.

What is claimed is:

1. In a free piston engine having a combustion piston reciprocal in a first cylinder and a working piston recip- (a) a central threaded bore positioned in said combustion piston;

(b) a rod rigidly attached to said working piston having an enlarged end positioned in said central threaded bore of said combustion piston said enlarged end being smaller in diameter than the diameter of said central threaded bore;

(c) a ring positioned on said rod between said enlarged end and said working piston, said ring having the central opening larger than said rod and smaller than said enlarged end, and said ring having peripheral threads engaged with said central threaded bore whereby said ring retains said enlarged end in said central bore providing a pivotal attachment between said pistons and allowing minor misalignment of said first and second cylinders; and

(d) a seal means mounted on said working piston, a relatively soft metallic surface on the periphery of said working piston contiguous to the wall of said second cylinder thereby allowing said working piston to wear into proper alignment when said first and second cylinders are misaligned, said metallic surface being softer than the material of said working piston.

References Cited UNITED STATES PATENTS 2,000,970 5/1935 McAllister 92175 2,057,158 10/1936 Moflitt 92152 X 2,793,089 5/ 1957 Anderson.

2,941,367 6/1960 Schwab 92151 X 2,963,175 12/1960 Thornhill 3084 X 2,991,003 7/1961 Petersen 92257 X 3,039,834 6/1962 Howe 308-4 3,070,022 12/ 1962 McCormack 92152 X 3,272,091 9/ 1966 Dziedzic 92152 FOREIGN PATENTS 970,693 6/ 1950 France.

MARTIN P. SCHWADRON, Primary Examiner I. C. COHEN, Assistant Examiner US. Cl. X.R. 92191 

